Disk drive unit with hydrodynamic fluid bearing unit and disk device with said drive unit

ABSTRACT

A disk drive unit includes a rotary member, which has a spindle, and has an information-recording disk fixedly mounted thereon, and a bearing unit rotatably supporting the spindle. The bearing unit includes a radial bearing device, provided in opposed relation to an outer peripheral surface of the spindle, and a thrust bearing device provided in opposed relation to a distal end surface of the spindle. The radial bearing device has a concentric arc-shaped bearing surface, which is concentric with the circular outer periphery of the spindle, and a non-concentric arc-shaped bearing surface which is non-concentric with the circular outer periphery of the spindle. The disk drive unit further includes a motor for imparting a rotational force to the spindle, and a lubricating fluid filled in the bearing unit.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 09/277,163, filedMar. 26, 1999, now U.S. Pat. No. 6,243,230, the subject matter of whichis incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a disk drive unit and a disk devicehaving this drive unit, and more particularly to a hydrodynamic fluidbearing unit for the disk drive unit.

Recently, in order to achieve the high-speed transfer of data andhigh-density recording, a motor in a magnetic disk drive unit has beenmore and more required to achieve a high-speed, high-precision rotation.In order to meet this requirement, a motor (as disclosed inJP-A-5-336696, JP-A-8-189525 and JP-A-9-200998), having a hydrodynamicbearing, has been proposed.

A motor in a magnetic disk drive unit is intensely required to have animproved shock resistance so that the function of the disk drive unitwill not be deteriorated when a personal computer, incorporating thedisk drive unit, is dropped from a desk or is fallen while it iscarried.

Particularly, a notebook-type personal computer can undergo an impactforce of about 1,000 G while it is used or carried, depending on themanner of handling it. And besides, since the notebook-type personalcomputer is driven by a battery, it requires a disk drive unit of thelow power consumption-type.

A groove bearing, wherein shallow grooves for producing a dynamicpressure are formed in a spindle, is proposed in JP-A-5-336696. Althoughthis groove bearing is excellent in high-speed operation and in accuracyof the spindle rotation, it has problems that the production cost ishigh and that the mass production can not be easily carried out. Thedepth of the dynamic pressure-producing grooves in the groove bearingare several microns, and when the grooves are deformed by an impactload, the adequate dynamic pressure cannot be produced, which results ina possibility that the unstable vibration occurs. A hydrodynamicthree-lobe bearing, disclosed in JP-A-8-189525 and JP-A-9-200998, canachieve high-speed, high precision rotation equivalent to that obtainedwith the above groove bearing. However, when an impact force of about1,000 G acts on this bearing, edge portions of the grooves can bedeformed, so that its bearing characteristics are deteriorated.

JP-A-8-189525 discloses a groove-type thrust bearing. When a bearingsurface of the groove-type thrust bearing is deformed by an impactforce, it is liable that a lubricating fluid is not-properly supplied tothe bearing surface.

The groove-type bearing supports or bears a thrust load at an endsurface of a spindle or bearing, and therefore is subjected to a largerfriction loss as compared with a ball bearing-type, and it is difficultto achieve a low power consumption design.

SUMMARY OF THE INVENTION

With the above problems of the prior art in view, it is an object ofthis invention to provide a disk drive unit provided with a bearing unitwhich has a small friction loss, and is excellent in shock resistanceand mass production efficiency.

Another object of the invention is to provide a magnetic disk deviceprovided with the above disk drive unit.

According to one aspect of the present invention, there is provided adisk drive unit comprising:

a rotary member having a spindle;

an information-recording disk being fixedly mounted on said rotarymember;

a bearing unit rotatably supporting the spindle, the bearing unitincluding

a radial bearing device provided in opposed relation to an outerperipheral surface of the spindle, the radial bearing device having aconcentric arc-shaped bearing surface that is concentric with thecircular outer periphery of the spindle, and a non-concentric arc-shapedbearing surface that is non-concentric with the circular outer peripheryof the spindle, and

a thrust bearing device provided in opposed relation to a distal endsurface of the spindle;

a motor for imparting a rotational force to the spindle; and

a lubricating fluid filled in the bearing unit.

The maximum distance between the spindle and each of the non-concentricarc-shaped bearing surfaces is 1.5 to 3 times larger than the distancebetween the spindle and each of the concentric arc-shaped bearingsurfaces.

The distal end surface of the spindle is formed into a flat surface, andthe thrust bearing device has a flat surface which is smaller indiameter than the spindle, and is held in opposed relationship with theflat distal end surface of the spindle.

In one form of the invention, the distal end surface of the spindle isrounded, and the thrust bearing device has a flat surface held inopposed relationship with the rounded distal end surface of the spindle.

In another form of the invention, the distal end surface of the spindleis rounded, and the thrust bearing device has a concave surface which issubstantially complementary to the rounded distal end surface of thespindle, and is held in opposed relationship with the rounded distal endsurface.

In one form of the disk drive unit of the invention, the radial bearingdevice comprises a plurality of radial bearings arranged in a directionof an axis of the spindle, and at least one of the plurality of radialbearings has only the concentric arc-shaped bearing surface, and each ofthe other radial bearings has a plurality of the non-concentricarc-shaped bearing surfaces and axial grooves each formed between theassociated adjacent non-concentric arc-shaped bearing surfaces.

In another form of the disk drive unit of the invention, the radialbearing device comprises a plurality of radial bearings arranged in adirection of an axis of the spindle, and each of the plurality of radialbearings has a plurality of the concentric arc-shaped bearing surfaces,a plurality of the non-concentric arc-shaped bearing surfaces and axialgrooves each formed between the associated adjacent non-concentricarc-shaped bearing surfaces, and the plurality of concentric arc-shapedbearing surfaces of the radial bearing extend ⅙ to ¾ of an innerperipheral surface of the radial bearing in a circumferential direction.

Preferably, the plurality of concentric arc-shaped bearing surfaces ofthe radial bearing extend about ⅓ of the inner peripheral surface of theradial bearing in the circumferential direction.

When viewed in a direction of an axis of the spindle, each of theplurality of concentric arc-shaped bearing surfaces is disposedsubstantially centrally between the associated adjacent axial grooves.Alternatively, each of the plurality of concentric arc-shaped bearingsurfaces is disposed adjacent to the associated axial groove.

According to another aspect of the invention, there is provided a diskdevice comprising:

a rotary member having a spindle;

an information-recording disk being fixedly mounted on the rotarymember;

a bearing unit rotatably supporting the spindle, the bearing unitincluding

a radial bearing device provided in opposed relation to an outerperipheral surface of the spindle, the radial bearing device having aconcentric arc-shaped bearing surface that is concentric with thecircular outer periphery of the spindle, and a non-concentric arc-shapedbearing surface that is non-concentric with the circular outer peripheryof the spindle, and

a thrust bearing device provided in opposed relation to a distal endsurface of the spindle,

a motor for imparting a rotational force to the spindle;

a lubricating fluid filled in the bearing unit;

a read/write head disposed in opposed relation to theinformation-recording disk; and

an actuator for positioning the head on said information-recording disk.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a first embodiment of amagnetic disk drive unit of the invention;

FIG. 2 is an enlarged, vertical cross-sectional view of a bearing unitof the first embodiment;

FIGS. 3 and 4 are transverse cross-sectional views of radial bearings ofthe first embodiment, respectively;

FIG. 5 is a vertical cross-sectional view of a second embodiment of amagnetic disk drive unit of the invention;

FIG. 6 is an enlarged, vertical cross-sectional view of a bearing unitof the second embodiment;

FIG. 7 is a transverse cross-sectional view of a radial bearing of thesecond embodiment;

FIG. 8 is a graph showing the relation between a bearing stiffness ofthe radial bearing and concentric arc-shaped bearing surfaces in thesecond embodiment;

FIG. 9 is a plan view of the radial bearing of the second embodiment;

FIG. 10 is a plan view of a modified radial bearing of the secondembodiment;

FIG. 11 is a view explanatory of a hydrodynamic effect of the modifiedradial bearing;

FIG. 12 is a plan view of a modified form of the radial bearing shown inFIG. 10;

FIG. 13 is a vertical cross-sectional view of a third embodiment of amagnetic disk drive unit of the invention;

FIG. 14 is an enlarged, vertical cross-sectional view of a bearing unitof the third embodiment;

FIG. 15 is an enlarged, vertical cross-sectional view of a bearing unitused in a fourth embodiment of a magnetic disk drive unit of theinvention;

FIG. 16 is a vertical cross-sectional view of a magnetic disk device ofthe invention, taken along line XVI—XVI in FIG. 17; and

FIG. 17 is a plan view of the magnetic disk device of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to thedrawings.

FIGS. 1 to 4 show a first embodiment of a magnetic disk drive unit ofthe present invention. Although this embodiment is directed to themagnetic disk drive unit, the present invention can be applied to anyother suitable device for driving or rotating an information-recordingmedium.

A spindle 1 is fixedly secured to a hub 13 having a cylindrical surfacefor mounting disks thereon. Magnetic disks 14 and 15 are fixedly securedto the hub 3 by a screw 22 through a disk clamp 18 and a spacer ring 16.A motor rotor (rotor magnet) 9, magnetized in a multi-pole pattern, isfixedly secured to an inner peripheral surface of the hub 13. Thespindle 1 is rotatably supported by radial bearings 2, 3 and 26 and athrust bearing 8. A retainer ring 7 is fixedly mounted on an end portionof the spindle 1.

A cover 17, the radial bearings 2, 3 and 26, the thrust bearing 8 andthe retainer ring 7 are provided in a bearing housing 5 made of anon-magnetic material, and a lubricating fluid 6 is sealed in thebearing housing 5. The bearing housing 5 and a motor stator 10, having amotor coil 11, are fixedly mounted on a motor casing 12.

The motor of this construction is a DC brushless motor, and the hub 13is driven by a rotating magnetic field, produced when the coil 11 isenergized, and a magnetic field possessed by the motor rotor 9magnetized in a multi-polar manner.

The bearing 26, having only a circular (arc-shaped) surface concentricwith the spindle 1, and the bearings 2 and 3, each havingnon-concentric, arc-shaped surfaces (see FIG. 4), are provided in thebearing unit of FIG. 2. A spacer 4 is provided between the bearings 2and 3. The distal end of the spindle 1 is formed into a generallysemi-spherical shape, and the flat thrust bearing 8 is disposed inopposed relation to this distal end.

The lubricating fluid 6 is sealed in the bearing housing 5, and thespindle 1 is supported in a non-contact manner by the radial bearings26, 2 and 3 through the lubricating fluid 6.

Ordinary lubricating oil may be used as the lubricating fluid 6.However, preferably, in order to achieve a sealing effect, a ring-shapedpermanent magnet, made of a rare earth element, is used as the spacer 4,and a magnetic fluid, having superfine magnetic powder (having aparticle size of about 0.01 μm) dispersed in lubricating oil, is used asthe lubricating fluid 6. With this construction, the magnetic fluid isattracted by the spacer 4 comprising the permanent magnet, and will notleak to the exterior of the bearing unit. The gap between the spindle 1and the radial bearings 2, 3 and 26, is very small on the order ofseveral micron meters, and therefore in a stationary condition, thesliding surfaces of the spindle and the radial bearings are wetted withthe magnetic fluid 6 because of a capillary phenomenon. Therefore, whenthe spindle 1 is driven, the sliding surfaces between the bearing andthe spindle are lubricated from the beginning of the rotation. Andbesides, the magnetic fluid 6, overflowing the radial bearing 2 becauseof the expansion of the volume of the magnetic fluid 6 by a temperaturerise and a hydrodynamic effect of the bearing, is attracted by thespacer 4 of a permanent magnet via grooves 19, 20 and 21 (FIG. 2) formedin bearing end surfaces and bearing outer peripheral surfaces of theradial bearings 2 and 3. Therefore, there is no fear that the magneticfluid 6 leaks to the exterior of the bearing unit.

FIG. 3 shows the configuration of the radial bearing 26 having only theconcentric circular (arc-shaped) bearing surface, and this radialbearing is a cylindrical bearing having a radius r. FIG. 4 shows theconfiguration of the radial bearing 2, 3 including the non-concentricarc-shaped bearing surfaces. More specifically, the radial bearing 2, 3has the three arc-shaped bearing surfaces, which are not concentric orcoaxial with the axis of the bearing, and have a radius (arc radius) R,and axial grooves 20′ each formed between the adjacent bearing surfaces.When an impact force is applied, the radial bearing 26 and the spindle 1come substantially into surface contact with each other since they havesubstantially the same curvature. In this case, if the lubricating fluidis provided on the bearing surface, a damping effect due to a squeezeaction effect is large, and therefore the spindle 1 and the radialbearing hardly come into direct contact with each other. During therotation, in addition to the effect of the radial bearing 26, thespindle 1 is supported in a non-contact manner by an oil film because ofthe hydrodynamic effect of the radial bearings 2 and 3, and thereforethe shock resistance is enhanced. And besides, since the spindle 1 issupported highly stiff by the oil film, the precise rotation can alwaysbe maintained.

Next, a second embodiment of a magnetic disk drive unit of the presentinvention will be described with reference to FIGS. 5 to 8.

FIG. 6 shows a bearing unit of this disk drive unit which differs fromthe bearing unit of FIG. 2 in that the radial bearing 26 is notprovided. The radial bearings 2′ and 3′ are different in configurationfrom the radial bearings 2 and 3 of the first embodiment in that abearing surface of the radial bearings 2′ and 3′ has portions forsurface contact with a spindle 1 upon being subjected to an impact load,as shown in FIG. 7.

More specifically, each of the radial bearings 2′ and 3′ has bearingsurfaces, which are concentric or coaxial with the axis of the spindle1, and have an arc radius r, and bearing surfaces which are notconcentric or coaxial with the axis of the spindle 1, and have an arcradius R. In the radial bearing 2′, 3′ shown in FIG. 7, the concentricarc-shaped bearing surfaces are represented by θ, and each of theseconcentric arc-shaped bearing surfaces is provided centrally betweenadjacent axial grooves 20′. When an external impact force is applied,these concentric arc-shaped bearing surfaces perform a damping effect.

Particularly when the concentric bearing surfaces θ, having the arcradius r, are suitably designed, the rigidity of the oil film for thebearing is about 1.5 times larger as compared with the conventionalhydrodynamic bearing, and therefore the more enhanced rotation precisioncan be obtained. With respect to the optimum dimension of the bearingsurfaces θ determined by the bearing stiffness, the sum of thedimensions of the bearing surfaces θ is in the range of about ⅓ of theentire bearing surface, as shown in FIG. 8. In order to enhance theshock resistance, the sum of the dimensions of the bearing surfaces θshould be about ¾ of the entire bearing surface though this slightlylowers the oil film stiffness of the bearing.

Even if the sum of the dimensions of the bearing surfaces θ is not morethan ⅙ of the entire bearing surface, similar results can be obtained,and preferably the sum of the dimensions of the bearing surfaces θ is ⅙to ¾. If the maximum gap a between the non-concentric arc-shaped bearingsurface and the spindle is 1.5 to 3 times larger than the gap c betweenthe concentric arc-shaped bearing surface and the spindle, the stiffnessof the oil film due to the hydrodynamic effect is increased.

As shown in FIG. 9, grooves 19 are formed in a bearing end surface ofthe radial bearing 2′, 3′, and grooves 20 are formed in the outerperipheral surface thereof. With this construction, a magnetic fluid 6is drawn by a magnetic attraction force of a spacer 4, comprising apermanent magnet, as described above.

The hydrodynamic radial bearing of the present invention can be formedor shaped using a sintered lubricant-containing bearing material, and bydoing so, the bearing unit, having good dimensional accuracy andexcellent mass production efficiency, can be provided.

As shown in FIG. 10, the concentric arc-shaped bearing surfaces can beprovided near to the grooves 20′, respectively.

The hydrodynamic effect of the hydrodynamic bearings, shown respectivelyin FIGS. 7 and 10, will be described. The bearing gap between thespindle 1 and the bearing surface is gently decreasing or narrowing asshown in the drawings. Therefore, when the spindle 1 rotates in adirection of arrow A, oil film pressures Pa, having a profile shown inFIG. 11, develop, and serve to hold the spindle 1 at the axis(centerline) of the bearing. In contrast, the gap between the spindle 1and the bearing surface at those portions designated by α is increasingin the direction of rotation, and therefore negative oil pressures Pbdevelop, and serve to lower the bearing stifness.

It is desirable for the bearing that the negative oil pressures Pb aresmall. However, the negative pressures serve to return the magneticfluid from the bearing end surface to the bearing surface. Thus, thenegative pressures serve to draw the magnetic fluid to the bearingsurface, and therefore if the dimension of α is set to about {fraction(1/10)} of the bearing surface, the magnetic fluid on the bearing endsurface can be returned to the bearing surface without hardly loweringthe performance of the bearing. In the bearing shown in FIG. 7, eachconcentric arc-shaped bearing surface is disposed centrally between theadjacent axial grooves 20′, and therefore this bearing is designed forsupporting the spindle rotating in opposite directions. On the otherhand, the bearing, shown in FIG. 10, is designed for supporting thespindle rotating in one direction.

In the above embodiment, although each of the radial bearings has thethree concentric arc-shaped bearing surfaces and the threenon-concentric arc-shaped bearing surfaces, each radial bearing may havethree or more arc-shaped bearing surfaces (for example, 4 to 5arc-shaped bearing surfaces as shown in FIG. 12). In this case, similareffects as described above can be achieved, and besides thehigher-precision rotation can be obtained, and this construction issuited for the type of magnetic disk drive unit required to have aparticularly-high rotation precision.

FIGS. 13 and 14 show a third embodiment of a disk drive unit of thepresent invention. In this embodiment, a distal end of a spindle 1 isflat, and a bearing surface of a thrust bearing 8 is flat, and issmaller in diameter than the spindle 1. A bearing unit of thisembodiment differs from the bearing unit of FIG. 6 in that an impactforce, applied in a thrust direction, is supported or borne by the flatsurface of the thrust bearing 8 and the distal end surface of thespindle 1. This construction has a higher shock resistance as comparedwith the thrust bearing of FIG. 6.

If the diameter of the contact surface of the thrust bearing 8 is ½ to ⅔of the diameter of the spindle 1, the deformation of the bearingsurface, developing upon application of an impact force of 1,000 G, ison the order of sub-micron meters, and therefore the precision of themagnetic disk device will not be deteriorated. Although a friction lossis slightly larger as compared with the bearing of the first embodiment,the smooth rotation can be achieved since an oil film is provided on thesliding surface.

FIG. 15 shows a fifth embodiment of a magnetic disk drive unit of thepresent invention. In this embodiment, a thrust bearing, having a flatsurface, is used in combination of a spindle 1, having a distal end of agenerally semi-spherical shape, as shown in FIG. 2, and a load,corresponding to an impact force of 1,000 G, is beforehand applied toform the bearing surface of the thrust bearing into a concave surfacehaving substantially the same semi-spherical shape as that of the distalend of the spindle 1.

When a load of several tens of kilograms is applied to a motor, having aconventional ball bearing, in an axial direction, a dent is formed on arolling surface of the bearing or balls. As a result, a rotating soundis increased, and also the rotation precision is much deteriorated. Onthe other hand, in the bearing unit of the present invention, a thrustload is supported or borne by the surface, that is, by the surfacecontact. Therefore, even if the bearing unit is press-fitted into themotor casing 12 while applying a load of several tens of kilograms tothe spindle 1, the bearing surface of the thrust bearing is hardlydeformed, and therefore the assembling efficiency of the magnetic diskdevice is greatly enhanced.

FIG. 16 shows a magnetic disk device of the present invention. Althoughthis embodiment is directed to the magnetic disk device, the presentinvention can be applied to any other suitable device or unit designedto store information in a rotating information-recording medium.

A magnetic head 104 is provided on one or each side of each magneticdisk (information-recording medium) 101 in opposed relation thereto.When the magnetic disk 101 is rotated, the magnetic head 104 flies amicroscopic distance off the magnetic disk 101, and in this conditionthe magnetic head 104 reads and writes magnetic information relative tothe magnetic disk 101. The magnetic head 104 is connected to a carriage106 through a load arm 105.

The carriage 106 is pivotally supported by a pivot bearing 107 so as tobe pivotally moved about an axis of this pivot bearing 107. With thisconstruction, a desired track on the magnetic disk 101 can be accessed.A voice-coil motor 108 is provided at that side of the carriage 106facing away from the magnetic heads 104, and moves the magnetic head 104at high speed to a desired track, and locates it at this track on themagnetic disk 101.

The load arms 105, the carriage 106, the pivot bearing 107 and thevoice-coil motor 108 jointly constitute an actuator. Generally, thepivot bearing 107 and the voice-coil motor 108 are pivotally mounted ona base 109 through pivot shafts. The provision of the load arms 105 maybe omitted. In order to protect these constituent parts from externaldirt and dust, a cover 110 is attached to the base 109, so that theconstituent parts are isolated from the exterior.

FIG. 17 is a plan view of the magnetic disk device of FIG. 16, with thecover removed.

A spindle 1 is rotatably mounted on the base 109, and the magnetic disks101 are fixedly mounted on the spindle 1 through a fixing member 18.Each magnetic head 104 is fixedly secured to the carriage 106, and isdisposed in proximity to the associated magnetic disk 101. The carriage106 is pivotally supported by the rotation shaft 107, and is driven bythe voice-coil motor 108. A signal, read by the magnetic head 104, istransmitted to the exterior of the sealed structure via a flexibleconnecting conductor 111. Adhesive members 114 and 115 are provided atan outlet port (through which the flexible connecting conductor 111passes) in the sealed structure, and hold the flexible connectingconductor 111 therebetween. Longer sides of the adhesive member 114 aredifferent in length from the longer sides of the adhesive member 115.The cover 110 (FIG. 16) is attached to the base 109, and with thisconstruction the sealed structure is provided.

Here, description will be made of effects achieved when using thebearing unit of the present invention (for example, the bearing unit ofFIG. 14) as the motor bearing unit in the magnetic disk device, will bedescribed.

In the magnetic disk device, as many magnetic disks 101 as possible arepackaged or received in the magnetic disk device having a limited height(vertical dimension) so as to obtain an increased memory capacity.Therefore, generally, a gap between the magnetic disk 101 and the loadarm 105, or a gap between the magnetic disk 101 and the carriage 106, ismicroscopic on the order of not more than 0.5 mm. When a hydrodynamicbearing is used as a motor bearing, gaps of radial bearings exist, andif these gaps are large, the magnetic disk 101 is much tilted uponapplication of an impact or the like, so that the magnetic disk 101 isbrought into contact with the load arm 105 or the carriage 106. As aresult, the magnetic disk 101 is damaged, and the magnetic head 104 isdamaged by powder dust produced by such contact. Therefore, in themagnetic disk device, it is necessary to reduce the gaps of the radialbearings as much as possible.

In the case of a groove bearing, an inner peripheral surface of thebearing is concentric (coaxial) and circular with respect to the axis ofthe bearing over an entire circumference thereof. Therefore, if abearing gap is reduced, a friction loss increases. On the other hand, inthe bearing unit of the present invention, the gap between eachconcentric arc-shaped bearing surface (which is concentric with respectto the axis of the bearing) and the outer peripheral surface of thespindle is reduced, and by doing so, the tilting of the disk due to agap (play) in the bearing portion can be suppressed. And besides, thegap between each non-concentric arc-shaped bearing surface (which isnon-concentric with respect to the axis of the bearing) is increased,and by doing so, the increase of the friction loss can be suppressed.Therefore, in the magnetic disk device of this embodiment, not only thebearing unit but also the magnetic disk device can be enhanced in shockresistance without increasing the power consumption.

In the hydrodynamic bearings of the present invention, the stiffness ofthe oil film for the bearing is high because of the above-mentionedeffects, and therefore the high-precision rotation can be maintained,and the excellent shock resistance is achieved. And besides, the bearinggap can be made larger as compared with a cylindrical bearing and theabove-mentioned conventional groove bearing, and therefore the viscousfriction loss is small, so that the low-loss design of the motor can beachieved.

Furthermore, since the thrust bearing has the flat surface, the shockresistance in the axial direction is excellent. The surface, bearing thethrust load, is smaller in diameter than the spindle, and therefore thefriction loss is smaller as compared with a thrust bearing of thehydrodynamic groove type, and there can be provided the magnetic diskdrive motor of a low power consumption-type suited for the magnetic diskdevice. And besides, the hydrodynamic bearings of the present inventioncan be produced using a sintered lubricant-containing bearing materialexcellent in mass production efficiency, and therefore there can beprovided the bearing unit wherein the dimensional accuracy of thebearing is high, and is suited for the magnetic disk device even fromthe viewpoint of the cost. And, the assembling precision and therotation precision are high, and the requirements of the high-densityand high-speed design of the magnetic disk device can be met.

By using the radial bearing and the thrust bearing of the presentinvention, there can be provided the magnetic disk device wherein thebearing is hardly deformed even if a large impact force is applied, andthe dimensional precision of the magnetic disk can be maintained, andthe excellent shock resistance is achieved. The bearing unit of thepresent invention is designed to bear a thrust load by the surface, andtherefore even if this bearing unit is press-fitted into the motorcasing 12 while applying a load of several tens of kilograms to thespindle 1, the thrust bearing surface is hardly deformed, and thereforethe assembling efficiency of the magnetic disk device is greatlyenhanced.

As described above, the bearing unit, the disk drive unit having thisbearing unit, and the magnetic disk device having this bearing unit, canmeet the requirements of the high-density recording of the magnetic diskmedium, the mass production and low-cost production of the magnetic diskdevice, and the long-lifetime and high-reliability design of the diskdrive unit. The bearing units, described and shown in the presentspecification and drawings, can be applied to a disk rotating (driving)mechanism used in a MD device, a CD-ROM device, a DVD-RAM device and thelike.

What is claimed is:
 1. A disk drive unit comprising: a rotary memberhaving a spindle; an information-recording disk being fixedly mounted onsaid rotary member; a bearing unit rotatably supporting said spindle,the bearing unit including a radial bearing device provided in opposedrelation to an outer peripheral surface of said spindle, the radialbearing device having a concentric arc-shaped bearing surface that isconcentric with said circular outer periphery of said spindle, and anon-concentric arc-shaped bearing surface that is non-concentric withsaid circular outer periphery of said spindle, and a thrust bearingdevice provided in opposed relation to a distal end surface of saidspindle, a motor for imparting a rotational force to said spindle; and alubricating fluid filled in said bearing unit.
 2. A disk drive unitaccording to claim 1, wherein the maximum distance between said spindleand said non-concentric arc-shaped bearing surfaces is 1.5 to 3 timeslarger than the distance between said spindle and said concentricarc-shaped bearing surfaces.
 3. A disk drive unit according to claim 1,wherein said distal end surface of said spindle is rounded, and saidthrust bearing device has a flat surface held in opposed relationshipwith said rounded distal end surface of said spindle.
 4. A disk devicecomprising: a rotary member having a spindle; an information-recordingdisk being fixedly mounted on said rotary member; a bearing unitrotatably supporting said spindle, the bearing unit including a radialbearing device provided in opposed relation to an outer peripheralsurface of said spindle, the radial bearing device having a concentricarc-shaped bearing surface that is concentric with said circular outerperiphery of said spindle, and a non-concentric arc-shaped bearingsurface that is non-concentric with said circular outer periphery ofsaid spindle, and a thrust bearing device provided in opposed relationto a distal end surface of said spindle, a motor for imparting arotational force to said spindle; a lubricating fluid filled in saidbearing unit; a read/write head disposed in opposed relation to saidinformation-recording disk; and an actuator for positioning said head onsaid information-recording disk.
 5. A disk device according to claim 4,wherein the maximum distance between said spindle and saidnon-concentric arc-shaped bearing surfaces is 1.5 to 3 times larger thanthe distance between said spindle and said concentric arc-shaped bearingsurfaces.
 6. A disk device according to claim 4, wherein said distal endsurface of said spindle is rounded, and said thrust bearing device has aflat surface held in opposed relationship with said rounded distal endsurface of said spindle.